Either create or choose your existing Shopify Store and Login to it
Open https://localhost:3000/shopify/install/new/[app-slug]?shop=[your-store].myshopify.com,
replace [app-slug] with your app slug and [your-store] with your store name. For example: https://localhost:3000/shopify/install/new/countdown-timer?shop=sergey2.myshopify.com
Click Install button
After successful installation, you will be redirected to the standalone page on your localhost. You will be able to use Shopify installation flow
Shopify app client ids and secrets are initialized here /config/environments/development.rb. We use same credentials for every active app for local development.
Please check that client_id and secret have correct values in your application.yml.
/app/controllers/shopify/install_controller.rb might get incorrect values for client_id and secret if you use different credentials for your app and installation will fail.